21,294 research outputs found
Smoothed Dissipative Particle Dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations
Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly
nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel
multiphase smoothed dissipative particle dynamics model. This model accounts
for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface
tension is modeled by imposing a pairwise force between SDPD particles. We show
that the relationship between the model parameters and surface tension,
previously derived under the assumption of zero thermal fluctuation, is
accurate for fluid systems at low temperature but overestimates the surface
tension for intermediate and large thermal fluctuations. To analyze the effect
of thermal fluctuations on surface tension, we construct a coarse-grained Euler
lattice model based on the mean field theory and derive a semi-analytical
formula to directly relate the surface tension to model parameters for a wide
range of temperatures and model resolutions. We demonstrate that the present
method correctly models the dynamic processes, such as bubble coalescence and
capillary spectra across the interface
Thermal Fluctuations in a Lamellar Phase of a Binary Amphiphile-Solvent Mixture: A Molecular Dynamics Study
We investigate thermal fluctuations in a smectic A phase of an
amphiphile-solvent mixture with molecular dynamics simulations. We use an
idealized model system, where solvent particles are represented by simple
beads, and amphiphiles by bead-and-spring tetramers. At a solvent bead fraction
of 20 % and sufficiently low temperature, the amphiphiles self-assemble into a
highly oriented lamellar phase. Our study aims at comparing the structure of
this phase with the predictions of the elastic theory of thermally fluctuating
fluid membrane stacks [Lei et al., J. Phys. II 5, 1155 (1995)]. We suggest a
method which permits to calculate the bending rigidity and compressibility
modulus of the lamellar stack from the simulation data. The simulation results
are in reasonable agreement with the theory
Evaluation of social personalized adaptive E-Learning environments : end-user point of view
The use of adaptations, along with the social aļ¬ordances of collaboration and networking, carries a great potential for improving e-learning experiences. However, the review of the previous work indicates current e-learning systems have only marginally explored the integration of social features and adaptation techniques. The overall aim of this research, therefore, is to address this gap by evaluating a system developed to foster social personalized adaptive e-learning experiences. We have developed our ļ¬rst prototype system, Topolor, based on the concepts of Adaptive Educational Hypermedia and Social E-Learning. We have also conducted an experimental case study for the evaluation of the prototype system from diļ¬erent perspectives. The results show a considerably high satisfaction of the end users. This paper reports the evaluation results from end user point of view, and generalizes our method to a component-based evaluation framework
Dynamic phenomena in superconducting oxides by ESR
Dynamic electron spin resonance (ESR) measurements compare the paramagnetic and antiferromagnetic (AF) properties of superconducting oxides in the range 4 K to room temperature, at 8 MHz and 9.36 GHz. Two are derivatives of YBa2Cu30 7: 1: Nd(Nd0.05Ba0.95 )2Cu30 7, Te0 =72 K and II: Y0.2Cao.8Sr2[Cu2(Tlo.5Pb0.5 )]07, Te0 =108 K and two are cases where AF ordering dominates the weak superconductivity: III: Nb01.1\u3e 1. 25 ~Teo~ 10 K and IV: La2Ni04.00, 70 K :::: Teo:::: 40 K. At temperatures 298:::: T:::: 64 K, the ESR absorption by I indicates orthorhombic symmetry. The peaks at Ke =2.06, gb =2.13, and Ka =2.24 are identified with the presence of 5% Nd3+( 41912 ) in the Ba layer because the characteristic Cu2+ impurity hyperfine structure is absent and the ESR signal disappears several degrees below Te. Near Te the ESR absorption is reduced by two orders of magnitude. Proximity effects give rise to interference fringes with period r1 ( T) independent of the field B and the rate of sweep dBzldt. ESR is observed below Te because flux penetrates the superconductor. The temperature dependence of r1 leads to an activation energy for the flux motion E0 (1)/R ~ 16 K and Ea (111)/R ~3 K =Te /4. In the superconducting state a coherent flux expulsion response to a change in B. from 500 mT to zero is observed in times T, = 8 to 10 s. The inverse rate of noise spikes due to flux expulsion, when the samples are cooled through Te in a magnetic field, varies from Tnoise=3.5 s for III to 21 s for IV. The microwave absorption spectra identify three temperature regimes: (i) For 3.5 K \u3c T \u3c T m T* \u3c Teo superconducting behavior was confirmed by the energy loss near zero magnetic field and the kinetics of high-field noise due to flux expulsion. Near g =2.00 ESR absorption is observed for all materials. A broad absorption near 50 to 100 mT at 9.36 GHz has been attributed to AF resonance. (ii) T m T* ~ T ~ Te identifies the range where flux motion gives rise to interference fringes in the ESR absorption. (iii) ESR and AF resonance are observed immediately after warming above Tc
Privacy-Preserving Outsourcing of Large-Scale Nonlinear Programming to the Cloud
The increasing massive data generated by various sources has given birth to
big data analytics. Solving large-scale nonlinear programming problems (NLPs)
is one important big data analytics task that has applications in many domains
such as transport and logistics. However, NLPs are usually too computationally
expensive for resource-constrained users. Fortunately, cloud computing provides
an alternative and economical service for resource-constrained users to
outsource their computation tasks to the cloud. However, one major concern with
outsourcing NLPs is the leakage of user's private information contained in NLP
formulations and results. Although much work has been done on
privacy-preserving outsourcing of computation tasks, little attention has been
paid to NLPs. In this paper, we for the first time investigate secure
outsourcing of general large-scale NLPs with nonlinear constraints. A secure
and efficient transformation scheme at the user side is proposed to protect
user's private information; at the cloud side, generalized reduced gradient
method is applied to effectively solve the transformed large-scale NLPs. The
proposed protocol is implemented on a cloud computing testbed. Experimental
evaluations demonstrate that significant time can be saved for users and the
proposed mechanism has the potential for practical use.Comment: Ang Li and Wei Du equally contributed to this work. This work was
done when Wei Du was at the University of Arkansas. 2018 EAI International
Conference on Security and Privacy in Communication Networks (SecureComm
Shot noise of inelastic tunneling through quantum dot systems
We present a theoretical analysis of the effect of inelastic electron
scattering on current and its fluctuations in a mesoscopic quantum dot (QD)
connected to two leads, based on a recently developed nonperturbative technique
involving the approximate mapping of the many-body electron-phonon coupling
problem onto a multichannel single-electron scattering problem. In this, we
apply the B\"uttiker scattering theory of shot noise for a two-terminal
mesoscopic device to the multichannel case with differing weight factors and
examine zero-frequency shot noise for two special cases: (i) a single-molecule
QD and (ii) coupled semiconductor QDs. The nonequilibrium Green's function
method facilitates calculation of single-electron transmission and reflection
amplitudes for inelastic processes under nonequilibrium conditions in the
mapping model. For the single-molecule QD we find that, in the presence of the
electron-phonon interaction, both differential conductance and differential
shot noise display additional peaks as bias-voltage increases due to
phonon-assisted processes. In the case of coupled QDs, our nonperturbative
calculations account for the electron-phonon interaction on an equal footing
with couplings to the leads, as well as the coupling between the two dots. Our
results exhibit oscillations in both the current and shot noise as functions of
the energy difference between the two QDs, resulting from the spontaneous
emission of phonons in the nonlinear transport process. In the "zero-phonon"
resonant tunneling regime, the shot noise exhibits a double peak, while in the
"one-phonon" region, only a single peak appears.Comment: 10 pages, 6 figures, some minor changes, accepted by Phys. Rev.
Position dependent photodetector from large area reduced graphene oxide thin films
We fabricated large area infrared photodetector devices from thin film of
chemically reduced graphene oxide (RGO) sheets and studied their photoresponse
as a function of laser position. We found that the photocurrent either
increases, decreases or remain almost zero depending upon the position of the
laser spot with respect to the electrodes. The position sensitive photoresponse
is explained by Schottky barrier modulation at the RGO film-electrode
interface. The time response of the photocurrent is dramatically slower than
single sheet of graphene possibly due to disorder from the chemically synthesis
and interconnecting sheets
Search for IR Emission from Intracluster Dust in A2029
We have searched for IR emission from the intracluster dust (ICD) in the
galaxy cluster A2029. Weak signals of enhanced extended emission in the cluster
are detected at both 24 and 70 micron. However, the signals are
indistinguishable from the foreground fluctuations. The 24 versus 70 micron
color map does not discriminate the dust emission in the cluster from the
cirrus emission. After excluding the contamination from the point sources, we
obtain upper limits for the extended ICD emission in A2029, 5 x 10^3 Jy/sr at
24 micron and 5 x 10^4 Jy/sr at 70 micron. The upper limits are generally
consistent with the expectation from theoretical calculations and support a
dust deficiency in the cluster compared to the ISM in our galaxy. Our results
suggest that even with the much improved sensitivity of current IR telescopes,
a clear detection of the IR emission from ICD may be difficult due to cirrus
noise.Comment: 5 pages, 4 figures, accepted by ApJ
GaAs-based Self-Aligned Stripe Superluminescent Diodes Processed Normal to the Cleaved Facet
We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real estate. Ā© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Differentially Private Model Selection with Penalized and Constrained Likelihood
In statistical disclosure control, the goal of data analysis is twofold: The
released information must provide accurate and useful statistics about the
underlying population of interest, while minimizing the potential for an
individual record to be identified. In recent years, the notion of differential
privacy has received much attention in theoretical computer science, machine
learning, and statistics. It provides a rigorous and strong notion of
protection for individuals' sensitive information. A fundamental question is
how to incorporate differential privacy into traditional statistical inference
procedures. In this paper we study model selection in multivariate linear
regression under the constraint of differential privacy. We show that model
selection procedures based on penalized least squares or likelihood can be made
differentially private by a combination of regularization and randomization,
and propose two algorithms to do so. We show that our private procedures are
consistent under essentially the same conditions as the corresponding
non-private procedures. We also find that under differential privacy, the
procedure becomes more sensitive to the tuning parameters. We illustrate and
evaluate our method using simulation studies and two real data examples
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